Many technological improvements in window and door design have been made available over the last several years. For instance, the insulating properties of newer window constructions are greatly improved over older window constructions, which can often provide significant energy cost savings to property owners. Consequently, a significant need has developed for replacing windows and doors during remodeling of older homes and buildings with newer, more efficient components.
One type of window replacement is referred to in the industry as "pocket replacement" of windows. In this application, the existing window is removed from its frame by removing enough molding on one side of the window to gain access to the full dimensions of the rough opening. One advantage of this application is that many of the trim pieces are left intact. However, many older windows have sills built into the wall at an angle relative to horizontal, and most newer windows are designed to be installed on a horizontal surface. According, there exists a need for replacement window structure that accommodates the sill angle of older window assemblies, so that the replacement window is securely supported by the preexisting sill and a satisfactory seal is formed therebetween.